Method and system for inspecting indirect bandgap semiconductor stucture

ABSTRACT

Methods ( 600 ) and systems ( 100 ) for inspecting an indirect bandgap semiconductor structure ( 140 ) are described. A light source ( 110 ) generates light ( 612 ) suitable for inducing photoluminescence in the indirect bandgap semiconductor structure ( 140 ). A short-pass filter unit ( 114 ) reduces long-wavelength light of the generated light above a specified emission peak. A collimator ( 112 ) collimates ( 616 ) the light. A large area of the indirect bandgap semiconductor structure ( 140 ) is substantially uniformly and simultaneously illuminated ( 618 ) with the collimated, short-pass filtered light. An image capture device ( 130 ) captures ( 620 ) images of photoluminescence simultaneously induced by the substantially uniform, simultaneous illumination incident across the large area for the indirect bandgap semiconductor structure. The photoluminescence images are image processed ( 622 ) to quantify spatially resolved specified electronic properties of the indirect bandgap semiconductor structure ( 140 ) using the spatial variation of the photoluminescence induced in the large area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 12/083,429filed Apr. 11, 2008, now issued as U.S. Pat. No. 8,064,054 B2, which wasfiled in the United States Patent and Trademark Office on Jun. 12, 2008as the U.S. National Phase of International Patent Application No.PCT/AU2006/001420 filed on Oct. 11, 2006. Said International PatentApplication No. PCT/AU2006/001420 published in the English language onApr. 19, 2007, as International Patent Publication No. WO 2007/041758,and claims priority to Patent Application No. 2005905598 filed inAustralia on Oct. 11, 2005. The contents of the foregoing applicationsare hereby incorporated by reference in their entireties.

TECHNICAL FIELD

The present invention relates generally to semiconductor testing andmore particularly to testing of indirect bandgap semiconductor material.

BACKGROUND

Photovoltaic manufacturing is a rapidly expanding market with typicalgrowth rates of greater than thirty percent (30%) per annum. Thepredominant sector of solar cell manufacturing is multi-crystallinewafer-based technology. In this industry, a significant proportion oftotal throughput is below specifications and is rejected, causingsubstantial financial losses to the industry each year. The productionof a solar cell involves a highly specialized sequence of processingsteps that starts with a bare semiconductor wafer, such as silicon.

Bel'kov, VV, et al, “Microwave-induced patterns in n-GaAs and theirphotoluminescence imaging”, Physical Review B, Vol. 61, No. 20, TheAmerican Physical Society, 15 May 2000, pp. 13698-13702 describes atechnique of photoluminescence (PL) imaging of n-GaAs. Photoluminescenceis the light emitted by a semiconductor material in response to opticalexcitation. Using the photoluminescence imaging, self-organized patternsof high-electron density are contactlessly studied in the homogenousn-GaAs layers under homogeneous microwave irradiation. The n-GaAscontactless sample is housed in a rectangular waveguide, which has ametallic mesh window for observation, coupled to a microwave generatorand is subjected to microwave irradiation. This assembly including then-GaAs sample is cooled to 4.2 K in a bath cryostat containing liquidhelium and illuminated uniformly with several red (620 nm) lightemitting diodes (LEDs) organized in a ring. The cryostat has a windowaligned with the metallic mesh window. A video camera is oriented facingthe sample, with optics and an interference 820 nm (long-pass) filterinterposed in that order between the cryostat window and the camera. Thecamera captures 3 mm×4 mm images, some of which show the formation ofdark spots in the photoluminescence from the sample under microwaveirradiation.

The system of Bel'kov can be used to test n-GaAs, which is a directbandgap semiconductor, Given the high magnitude of photoluminescenceefficiency in such a semiconductor the n-GaAs sample allows relativelylow powered LEDs to be used as light sources for inducingphotoluminescence, in which the source illumination diverges. Also, thearrangement of the waveguide and cryostat windows limits the viewingarea of the camera. Disadvantageously, this only permits small areas (3mm×7 mm) to be tested. Further, the system requires samples to be testedat low temperatures produced by a cryostat. The configuration of Bel'kovpermits source illumination from the LEDs to be captured by the videocamera. The long-pass filter is intended to block illumination from theLEDs and to transmit photoluminescence above 820 nm to the camera, butalso transmits any illumination from the LEDs above 820 nm to thecamera. For n-GaAs samples, the high efficiency photoluminescencegenerated greatly exceeds any undesired illumination from the LEDs. Inview of these and other limitations, the system of Bel'kov is not suitedfor testing indirect bandgap semiconductors.

Masarotto, et al, “Development of an UV scanning photoluminescenceapparatus for SiC characterization”, Eur J AP 20, 141-144, 2002,describes an adapted scanning PL apparatus for characterizing SiC. PLmapping is obtained by scanning the sample using an x-y stage with a 1μM step and a doubled Ar⁺ laser beam focused by a microscope objective,with a spot diameter of 4 μM. Either integrated PL intensity orspectrally resolved PL can be obtained. This system scans PL in apoint-by-point fashion. Such a system disadvantageously only permits asmall area, i.e. a point, to be tested at any given time due to thescanning operation. Photoluminescence cannot be simultaneously capturedacross a large area of the sample under homogeneous illumination acrossthe large area, which would better approximate operating conditions of asemiconductor device. Further, such a system is disadvantageously slowdue to the scanning operation of the system.

A need therefore exists for an inspection system for indirect bandgapsemiconductor structures, especially silicon, including bare orpartially processed wafers that might otherwise result in a rejectedsolar cell.

SUMMARY

In accordance with an aspect of the invention, there is provided amethod of inspecting an indirect bandgap semiconductor structure. Themethod comprises the steps of: generating light suitable for inducingphotoluminescence in the indirect bandgap semiconductor structure;short-pass filtering the light to reduce long-wavelength light of thegenerated light above a specified emission peak; collimating the light;substantially uniformly and simultaneously illuminating a large area ofthe indirect bandgap semiconductor structure with the collimated,short-pass filtered light; capturing images of photoluminescencesimultaneously induced by the substantially uniform, simultaneousillumination incident across the large area of the indirect bandgapsemiconductor structure using an image capture device capable ofcapturing simultaneously the induced photoluminescence; and imageprocessing the photoluminescence images to quantify spatially resolved,specified electronic properties of the indirect bandgap semiconductorstructure using the spatial variation of said photoluminescence inducedin said large area.

The indirect bandgap semiconductor may comprise silicon. The structuremay comprise a bare or partially processed wafer of indirect bandgapsemiconductor material, at least one partially formed electronic device,or a bare or partially processed silicon-on-insulator (SOI) structure.The electronic device may be a photovoltaic device.

The short-pass filtering step may be implemented using one or moreshort-pass filters. The short-pass filtering step may be implementedusing dielectric mirrors, which reflect short wavelength light to beused and transmit unwanted long wavelength components. The short-passfiltering step may reduce by a factor of about 10 or more the totalphoton flux in a long-wavelength tail of the generated light, thelong-wavelength tail beginning at a wavelength that is about ten percent(10%) higher than a longest wavelength emission peak of a source forgenerating the light.

The illuminated area of the indirect bandgap semiconductor structure maybe equal to or greater than about 1.0 cm².

The method may further comprise the step of homogenizing the generatedlight.

The method may be performed at room temperature.

The generated light may be monochromatic or substantially monochromaticlight. The light may be generated by at least one laser, laser diode,laser diode array, or high-powered light emitting diode (LED).Alternatively, the light may be generated by an array of light emittingdiodes (LEDs) or a broad spectrum lamp and filtered to limit thespectrum of the light.

The total optical power of the light may exceed about 1 Watt.

A source of the generated light may be oriented toward the surface ofone side of the structure for illumination of that surface and the imagecapture device is oriented toward the same surface for capturing theimages of photoluminescence from that surface. Alternatively, a sourceof the generated light is oriented toward the surface of one side of thestructure for illumination of that surface and an image capture deviceis oriented toward the surface of an opposite side of the structure forcapturing the images of photoluminescence from the surface of theopposite side.

The method may further comprise the step of long pass filtering thephotoluminescence induced in the silicon structure. The structure mayact as long-pass filter of the incident light used for excitation of thephotoluminescence. One or more long pass filters may be used incombination with the image capture device. The image capture device maycomprise a focusing element and a focal plane array of light sensitiveelectronic elements. The focal plane array of light sensitive electronicelements may comprise an array of charge coupled devices (CCDs). Thefocal plane array may be made from silicon. The focal plane array oflight sensitive electronic elements may be made from InGaAs. The focalplane array may be cooled.

The image capture device may comprise a pixel detector. The pixeldetector may be a contact pixel detector coupled to a surface of thestructure.

The image capture device may be a pixel detector or an array of chargecoupled devices (CCDs), and a tapered fiber bundle may be coupledbetween a surface of the structure and the pixel detector or the CCDarray.

The specified electronic properties comprise one or more of local defectdensities, local shunts, local current-voltage characteristics, localdiffusion length, and local minority carrier lifetime.

In accordance with another aspect of the invention, there is provided asystem for inspecting an indirect bandgap semiconductor structure. Thesystem comprises: a light source for generating light suitable forinducing photoluminescence in the indirect bandgap semiconductorstructure; a short-pass filter unit disposed between the light sourceand the indirect bandgap semiconductor structure to reducelong-wavelength light of the generated light above a specified emissionpeak; a collimator disposed between the light source and the indirectbandgap semiconductor structure, the collimated, short-pass filteredlight substantially uniformly and simultaneously illuminating a largearea of the indirect bandgap semiconductor structure; an image capturedevice oriented towards the indirect bandgap semiconductor structure forcapturing images of photoluminescence induced by said substantiallyuniform, simultaneous illumination incident across said large area ofthe indirect bandgap semiconductor structure by incident light.

The system may further comprise an image processor for processing thephotoluminescence images to quantify spatially resolved, specifiedelectronic properties of the indirect bandgap semiconductor structure.

The indirect bandgap semiconductor may comprise silicon. The structuremay comprise a bare or partially processed wafer of indirect bandgapsemiconductor material, at least one partially formed electronic device,or a bare or partially processed silicon-on-insulator (SOI) structure.The electronic device may be a photovoltaic device.

The short-pass filter unit may comprise one or more short-pass filters.The short-pass filter unit may comprise one or more dielectric mirrors,which reflect short wavelength light to be used and transmit unwantedlong wavelength components. The short-pass filter unit may reduce by afactor of about 10 or more the total photon flux in a long-wavelengthtail of the generated light, the long-wavelength tail beginning at awavelength that is about ten percent (10%) higher than a longestwavelength emission peak of the light source for generating the light.

The illuminated area of the indirect bandgap semiconductor structure maybe equal to or greater than about 1.0 cm².

The system may further comprise a beam homogenizer to homogenize theincident light across the illuminated area.

The system may inspect the indirect bandgap semiconductor sample at roomtemperature.

The generated light may be monochromatic or substantially monochromaticlight.

The light source may comprise at least one laser, laser diode, laserdiode array, or high-powered light emitting diode (LEDs), an array oflight emitting diodes (LEDs), or a broad spectrum lamp in combinationwith one or more filters to limit the spectrum of the light.

The total optical power of the light may exceed about 1 Watt.

The light source may be oriented toward the surface of one side of thestructure for illumination of that surface and the image capture deviceis oriented toward the same surface for capturing the images ofphotoluminescence from that surface. Alternatively, the light source maybe oriented toward the surface of one side of the structure forillumination of that surface and the image capture device is orientedtoward the surface of an opposite side of the structure for capturingthe images of photoluminescence from the surface of the opposite side.

The structure may act as long-pass filter of the incident light used forexcitation of the photoluminescence.

The system may further comprise one or more long pass filters for use incombination with the image capture device. The image capture device maycomprise a focusing element and a focal plane array of light sensitiveelectronic elements. The focal plane array of light sensitive electronicelements may comprise an array of charge coupled devices (CCDs). Thefocal plane array may be made from silicon. The focal plane array oflight sensitive electronic elements may be made from InGaAs. The focalplane array may be cooled.

The image capture device may comprise a pixel detector. The pixeldetector may be a contact pixel detector coupled to a surface of thestructure.

The image capture device may be a pixel detector or an array of chargecoupled devices (CCDs), and may further comprise a tapered fiber bundlecoupled between a surface of the structure and the pixel detector or theCCD array.

The specified electronic properties may comprise one or more of localdefect densities, local shunts, local current-voltage characteristics,local diffusion length, and local minority carrier lifetime.

In accordance with yet another aspect of the invention, there isprovided a method of inspecting a silicon structure. The methodcomprises the steps of: generating light suitable for inducingphotoluminescence in the silicon structure; short-pass filtering thelight to reduce long-wavelength light of the generated light above aspecified emission peak; collimating the light; substantially uniformlyand simultaneously illuminating a large area of one side of the siliconstructure with the collimated, short-pass filtered light; and capturingimages of photoluminescence simultaneously induced by said substantiallyuniform, simultaneous illumination incident across said large area ofthe silicon structure using an image capture device capable of capturingsimultaneously said induced photoluminescence.

The method may further comprise the step of image processing thephotoluminescence images to quantify spatially resolved, specifiedelectronic properties of the silicon structure.

The structure comprises a bare or partially processed wafer of siliconmaterial, at least partially formed photovoltaic device made fromsilicon, or a bare or partially processed silicon-on-insulator (SOI)structure.

The short-pass filtering step may be implemented using one or moreshort-pass filters. The short-pass filtering step may be implementedusing dielectric mirrors, which reflect short wavelength light to beused and transmit unwanted long wavelength components.

The short-pass filtering step may reduce by a factor of about 10 or morethe total photon flux in a long-wavelength tail of the generated light,the long-wavelength tail beginning at a wavelength that is about tenpercent (10%) higher than a longest wavelength emission peak of a lightsource for generating the light.

The illuminated area of the silicon structure may be equal to or greaterthan about 1.0 cm².

The method may further comprise the step of homogenizing the generatedlight.

The method may be performed at room temperature.

The generated light may be monochromatic or substantially monochromaticlight. The light may be generated by at least one laser, laser diode,laser diode array, high-powered light emitting diode (LED), an array oflight emitting diodes (LEDs), or a broad spectrum lamp and filtered tolimit the spectrum of the light.

The total optical power of the light may exceed about 1 Watt.

A source of the generated light may be oriented toward the surface ofone side of the structure for illumination of that surface and an imagecapture device is oriented toward the same surface for capturing theimages of photoluminescence from that surface. Alternatively, a sourceof the generated light is oriented toward the surface of one side of thestructure for illumination of that surface and an image capture deviceis oriented toward the surface of an opposite side of the structure forcapturing the images of photoluminescence from the surface of theopposite side.

The method may further comprise the step of long pass filtering thephotoluminescence induced in the silicon structure. The structure mayact as long-pass filter of the incident light used for excitation of thephotoluminescence. One or more long pass filters may be used incombination with the image capture device.

The image capture device may comprise a focusing element and a focalplane array of light sensitive electronic elements. The focal planearray of light sensitive electronic elements may comprise an array ofcharge coupled devices (CCDs). The focal plane array may be made fromsilicon. The focal plane array of light sensitive electronic elementsmay be made from InGaAs. The focal plane array may be cooled.

The image capture device may comprise a pixel detector. The pixeldetector may be a contact pixel detector coupled to a surface of thestructure.

The image capture device may be a pixel detector or an array of chargecoupled devices (CCDs), and a tapered fiber bundle may be coupledbetween a surface of the structure and the pixel detector or the CCDarray.

The specified electronic properties comprise one or more of local defectdensities, local shunts, local current-voltage characteristics, localdiffusion length, and local minority carrier lifetime.

In accordance with still another aspect of the invention, there isprovided a system for inspecting a silicon structure. The systemcomprises: a light source for generating light suitable for inducingphotoluminescence in the silicon structure; a short-pass filter unitdisposed between the light source and the silicon structure to reducelong-wavelength light of the generated light above a specified emissionpeak; a collimator disposed between the light source and the siliconstructure, short-pass filtered light substantially uniformly andsimultaneously illuminating a large area of one side of the siliconstructure; and an image capture device for capturing images ofphotoluminescence simultaneously induced by said substantially uniform,simultaneous illumination incident across the large area of the siliconstructure by incident light.

The system may further comprise an image processor for processing thephotoluminescence images to quantify spatially resolved, specifiedelectronic properties of the silicon structure.

The structure may comprise a bare or partially processed wafer ofsilicon material, at least partially formed photovoltaic device madefrom silicon, or a bare or partially processed silicon-on-insulator(SOI) structure.

The short-pass filter unit may comprise one or more short-pass filters.The short-pass filter unit may comprise one or more dielectric mirrors,which reflect short wavelength light to be used and transmit unwantedlong wavelength components.

The one or more short-pass filters reduce by a factor of about 10 ormore the total photon flux in a long-wavelength tail of the generatedlight, the long-wavelength tail beginning at a wavelength that is aboutten percent (10%) higher than a longest wavelength emission peak of alight source for generating the light.

The illuminated area of the silicon structure may be equal to or greaterthan about 1.0 cm².

The system may further comprise a homogenizer for homogenizing thegenerated light.

The system may inspect the silicon structure at room temperature.

The generated light may be monochromatic or substantially monochromatic.

The light source may be comprise at least one laser, laser diode, laserdiode array, high-powered light emitting diode (LED), an array of lightemitting diodes (LEDs), or a broad spectrum lamp and filtered to limitthe spectrum of the light.

The total optical power of the light may exceed about 1 Watt.

The light source may be oriented toward the surface of one side of thesilicon structure for illumination of that surface and the image capturedevice is oriented toward the same surface for capturing the images ofphotoluminescence from that surface. Alternatively, the light source maybe oriented toward the surface of one side of the silicon structure forillumination of that surface and the image capture device is orientedtoward the surface of an opposite side of the structure for capturingthe images of photoluminescence from the surface of the opposite side.

The system may further comprise one or more long-pass filters for longpass filtering the light entering the image capture device.

The image capture device may comprise a focusing element and a focalplane array of light sensitive electronic elements. The focal planearray of light sensitive electronic elements may comprise an array ofcharge coupled devices (CCDs). The focal plane array may be made ofsilicon. The focal plane array of light sensitive electronic elementsmay be made from InGaAs. The focal plane array may be cooled.

The image capture device may comprise a pixel detector. The pixeldetector may be a contact pixel detector coupled to a surface of thestructure.

The image capture device may be a pixel detector or an array of chargecoupled devices (CCDs), and may further comprise a tapered fiber bundlecoupled between a surface of the structure and the pixel detector or theCCD array.

The specified electronic properties may comprise one or more of localdefect densities, local shunts, local current-voltage characteristics,local diffusion length, and local minority carrier lifetime.

Other aspects of this system may be implemented in accordance with thedetails of the foregoing method.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention are described hereinafter with reference tothe drawings, in which:

FIG. 1 is a block diagram of a system for inspecting an indirect bandgapsemiconductor structure in accordance with an embodiment of theinvention;

FIG. 2 is a block diagram of a system for inspecting an indirect bandgapsemiconductor structure in accordance with another embodiment of theinvention;

FIG. 3 is a block diagram of a system for inspecting an indirect bandgapsemiconductor structure in accordance with a further embodiment of theinvention;

FIG. 4 is a block diagram of a system for inspecting an indirect bandgapsemiconductor structure in accordance with yet another embodiment of theinvention;

FIG. 5 is a block diagram of a system for inspecting an indirect bandgapsemiconductor structure in accordance with a further embodiment of theinvention;

FIG. 6 is a flow diagram of a method of inspecting an indirect bandgapsemiconductor structure in accordance with an embodiment of theinvention; and

FIG. 7 is a block diagram of a system for impacting an indirect bandgapsemiconductor structure in accordance with still another embodiment ofthe invention.

DETAILED DESCRIPTION

Methods and systems are disclosed for inspecting indirect bandgapsemiconductor structures. In the following description, numerousspecific details, including indirect bandgap semiconductor materials,image capture devices, and the like are set forth. However, from thisdisclosure, it will be apparent to those skilled in the art thatmodifications and/or substitutions may be made without departing fromthe scope and spirit of the invention. In other circumstances, specificdetails may be omitted so as not to obscure the invention.

Where reference is made in any one or more of the accompanying drawingsto steps and/or features, which have the same or like referencenumerals, those steps and/or features have for the purposes of thisdescription the same function(s) or operation(s), unless the contraryintention appears.

In the context of this specification, the word “comprising” has anopen-ended, non-exclusive meaning: “including principally, but notnecessarily solely”, but neither “consisting essentially of” nor“consisting only of”. Variations of the word “comprising”, such as“comprise” and “comprises”, have corresponding meanings.

1. Introduction

The embodiments of the invention provide inspection systems and methodsfor indirect bandgap semiconductor structures, including bare orpartially processed wafers. In particular, the systems and methods areparticularly suited for testing silicon structures, including bare orpartially processed wafers, partially fabricated silicon devices, bareor partially processed silicon-on-insulator (SOT) structures, and fullyfabricated silicon devices. The systems and methods are able tocontactlessly detect defects existing in the bare wafer prior toprocessing and throughout various fabrication stages through to thefinished semiconductor device, including devices that have been partlymetallized. By contactless, what is meant is that no electrical contactis required. For example, the embodiments of the invention can inspectsilicon structures and identify defects, which might otherwise result inthe structure being a rejected solar cell or other photovoltaic device.The systems and methods are also able to contactlessly determinespatially resolved material parameters, such as local defect densities,local shunts, local current-voltage characteristics, local diffusionlength, and local minority carrier lifetime after various processingsteps. The embodiments of the invention utilize the photoluminescence(PL) simultaneously induced across large areas of indirect bandgapsemiconductor structures to characterize the indirect bandgapsemiconductor structures.

In the embodiments of the invention, instead of analyzing the spectralcontent of the photoluminescence, the spatial variation of aphotoluminescence signal is used to obtain information about the qualityof the indirect bandgap semiconductor material. As the embodiments ofthe invention are particularly well suited to use with silicon, thedescription hereinafter refers to silicon structures, including siliconwafers. However, in the light of this disclosure, those skilled in theart will appreciate that the embodiments of the invention may bepracticed with other indirect bandgap semiconductors, such as germaniumand alloys of silicon and germanium. The systems and methods forinspecting silicon structures may allow for wafers to be inspected atrates suitable for industrial application (e.g., about 1 wafer persecond).

In the embodiments of the invention, light suitable for inducingphotoluminescence in silicon is generated and used to illuminatesubstantially uniformly a large area of a silicon sample. The term“substantially uniform” is used to describe the light, which may equallyreferred to as homogeneous, since as a practical matter illumination isnot perfectly uniform. For example, monochromatic or substantiallymonochromatic light (e.g. from a laser or laser diode) or partlyfiltered light from a broad spectrum light source (e.g. a flash lamp)may be used to illuminate the silicon sample. In particular, short-passfiltering is applied to the generated light to greatly reduce thespectral content of the light above a specified wavelength. An opticalarrangement is used in combination with the light source to illuminatehomogeneously a large area of the wafer. Preferably, the entire waferarea to be investigated is illuminated homogeneously. Thephotoluminescence induced simultaneously in the silicon structure by thesubstantially uniform, simultaneous incident light is captured using animage capture device capable of capturing simultaneously the inducedphotoluminescence. The image capture device preferably comprises afocusing element and a focal plane array of light sensitive electronicelements. The focal plane array of light sensitive electronic elementsmay comprise a charge coupled device (CCD) array. The focal plane arraymay be made from silicon. However, as described hereinafter, otherdevices besides a CCD array may be practiced without departing from thescope and spirit of the invention. The image capture device may be usedin combination with optical imaging and/or filtering arrangements.

In some embodiments of the invention, the silicon wafer is illuminatedfrom one side using the noted light source, and the photoluminescenceinduced in the large area of the wafer by the incident light is capturedfrom the opposite side of the silicon wafer. In other embodiments, thephotoluminescence is captured from the same side of the silicon waferthat is illuminated. Imaging and image processing techniques are thenapplied to the captured PL images. Analyzing the data allows determininglocal material parameters within the silicon structure using the spatialvariation of the photoluminescence induced in the large area. This mayallow identifying silicon structures that are defective at an earlystage in device manufacturing to reject those structures that will berejected ultimately.

While the embodiments of the invention are suited for industrialapplication, the methods and systems can be applied to scientificresearch. Photoluminescence images may be used for example to determinelocal defect rich areas, local shunts, local current-voltagecharacteristics, local diffusion length, and/or local minority carrierlifetime, which may be of benefit not only in photovoltaics, but also inother fields such as microelectronics. The embodiments of the inventioncan be applied in contactless mode and are therefore particularly suitedto inspect local material parameters after individual processing steps.The embodiments of the invention are described in greater detailhereinafter.

2. Inspecting an Indirect Bandgap Semiconductor Structure

FIG. 6 is a high-level flow diagram illustrating a method 600 ofinspecting an indirect bandgap semiconductor structure. In step 610,processing commences. In step 612, light suitable for inducingphotoluminescence in the indirect bandgap semiconductor structure isgenerated. In step 614, the light is short-pass filtered to reducelong-wavelength light of the generated light above a specified emissionpeak. In step 616, the light is collimated. Steps 614 and Step 616 canalso be carried out in the reverse order. In step 618, a large area ofthe indirect bandgap semiconductor structure is substantially uniformlyand simultaneously illuminated with the collimated, short-pass filteredlight. In step 620, images of photoluminescence simultaneously inducedby the substantially uniform, simultaneous illumination incident acrossthe large area of the indirect bandgap semiconductor structure arecaptured using an image capture device capable of capturingsimultaneously the induced photoluminescence. In step 622, thephotoluminescence images are image processed to quantify specifiedelectronic properties of the indirect bandgap semiconductor structureusing the spatial variation of the photoluminescence induced in thelarge area. Processing then terminates in step 622. The foregoing methodof inspecting an indirect bandgap semiconductor structure is expoundedupon hereinafter with reference to several embodiments implementingvarious systems for inspecting such structures.

3. Illumination and Imaging on Opposite Sides

FIG. 1 illustrates a system 100 for inspecting a silicon structure 140,which is preferably a silicon wafer. Photovoltaic and microelectronicdevices can be fabricated in a number of stages on such a silicon wafer.The system 100 of FIG. 1 can be used to inspect a bare or partiallyprocessed wafer, a wafer that has undergone any number of processingsteps to form a photovoltaic device such as a solar cell or amicroelectronic device, and a finished device resulting from thefabrication process. For example, the silicon wafer 140 may havedimensions of 150 mm×150 mm 0.25 mm. The structure may comprise a bareor partially processed silicon-on-insulator (SOI) structure with asubstrate that is transparent to the incident light. The inspectionmethod can be performed at room temperature. For ease of discussion, thesilicon structure is simply referred to hereinafter as the siliconsample.

The system 100 comprises a light source 110, a short-pass filter unit114, and an image capture device 122. The short-pass filter unit 114 maycomprise one or more short-pass filters. A short-pass filter passesthrough the excitation light and absorbs or reflects an unwanted longwavelength emission(s). Examples of short-pass filters include coloredfilters and dielectric interference filters. Alternatively, a dielectricmirror may be used (e.g. under 45 degrees) that reflects that part ofthe light that is to be used and transmits the unwanted long wavelengthlight. The short-pass filter unit may also comprise a combination ofshort pass filters and dielectric mirrors.

The system also comprises a collimator 112 and may comprise ahomogenizer 116, which is a device for converting a collimated beam oflight that has non-uniform intensity into a uniformly illuminated regionof a plane perpendicularly incident to the collimated beam. Examplesinclude cross cylindrical lens array(s) and a micro lens array. Acollimator may be lenses of various sorts. In the embodiment of FIG. 1,the elements of the system 100 are arranged as follows: a light source110 facing the silicon sample 140, the collimator 112, the short-passfilter unit 114, and the homogenizer 116 optically aligned in thatsequence. In another embodiment of the invention, the ordering of thecollimator 112 and the short-pass filter unit 114 may be reversed. Afield lens 117 may be used between the homogenizer and the siliconsample. The elements are spaced apart from the silicon sample 140 sothat a large area of the sample 140 can be illuminated homogeneously.

The light source 110 generates light suitable for inducingsimultaneously photoluminescence across a large area of the siliconsample 140. The total optical power of the generated light may exceed1.0 Watt. Light sources of higher power are able to more quickly andintensely induce photoluminescence in the silicon sample 140. The lightsource 110 may generate monochromatic or substantially monochromaticlight. The light source 110 may be at least one laser. For example, an808 nm diode laser may be used to generate monochromatic light. Two ormore lasers with different principal wavelengths may also be practiced.Another light source 110 may comprise a broad spectrum light source(e.g., a flash lamp) combined with suitable filtering to provide partlyfiltered light. Still another light source 110 may be a high-poweredlight emitting diode (LED). Yet another light source 110 may comprise anarray of light emitting diodes (LED). For example, such an LED array maycomprise a large number (e.g. 60) of LEDs in a compact array withheatsinking. Other high powered light sources may be practiced withoutdeparting from the scope and spirit of the invention.

The light from the light source 110 is collimated into parallel beams bya collimator or collimator unit 112, which may comprise more than oneelement. Short-pass filtering is applied to the generated light. Thismay be done using an interference short-pass filter unit 114 comprisingone or more filter elements. Short-pass filtering the generated lightreduces long-wavelength light above a specified emission peak. Theshort-pass filter 114 may reduce by a factor of about 10 or more thetotal photon flux in a long-wavelength tail of the generated light. Thelong-wavelength tail may begin at a wavelength that is about ten percent(10%) higher than a longest wavelength emission peak of the light source110. For example, the filtering may remove unwanted spectrum componentssuch as infra-red components with wavelengths in the range of 900 nm to1800 nm or a subrange of that range. Multiple short-pass filters may beused because one filter may not be sufficient itself to remove or reduceunwanted spectrum components. The short-pass filters may be implementedat numerous different positions in the overall combination of opticalelements between the light source 110 and the silicon sample 140. Forexample, filters may be positioned between the homogenizer 116 and thefield lens 117. If more than one short pass filter is used, then one ormore of the filters may be arranged so that they are tilted under someangle against the optical axis of the collimated beam to avoid multiplereflections of the reflected light. The short-pass filtered andcollimated light may then be homogenized by a homogenizer 116 tohomogeneously illuminate a large area of the silicon sample 140. Howeverthe ordering of the steps may be altered. The homogeneously illuminatedarea of the silicon sample may be greater than or equal to about 1.0cm². The homogenizer 116 distributes the collimated beams evenly acrossthe surface of the silicon sample 140.

The homogeneous illumination incident on the surface of the siliconsample 140 is sufficient to induce photoluminescence simultaneously inthe silicon sample. This photoluminescence is represented in FIG. 1 byarrows or rays emanating from the opposite surface of the silicon sample140. For ease of illustration only, corresponding photoluminescence isnot shown emanating from the first surface of the silicon sample 140that the light source 110 is oriented towards. The externalphotoluminescence quantum efficiency of silicon can be very low (of theorder of <10⁻⁶). An image capture device 130 captures images of thephotoluminescence simultaneously induced in the silicon sample. Theshort pass filter unit 114 reduces or removes incident light from thelight source 110 from being received by the image capture device 130.Light source tail radiation may be of the order of 10⁻⁴ of a sourcepeak, which can significantly exceed the PL efficiency of silicon (ofthe order of 10⁻⁶) in contrast to that of direct bandgap semiconductorslike AlGaAs (of the order of 10⁻²). In this embodiment, the light source110 is oriented toward the surface of one side of the silicon sample 140for illumination of that surface. The silicon sample 140 acts aslong-pass filter of the generated light illuminating the silicon sample140. The image capture device 130 is oriented toward the surface of theopposite side of the silicon sample 140 for capturing the PL images fromthat opposite side. A long-pass filter unit 118 may be used incombination with the image capture device 130. This filter unit 118 maybe optional, since the silicon wafer 140 may remove any residual lightfrom the light source 110 dependent upon the wafer thickness andwavelengths of incident light. The image capture device 130 (and thelong-pass filter 118) is suitably spaced apart from the other surfacethat the image capture device 130 is facing.

The image capture device 130 comprises a focusing element 120 (e.g. oneor more lenses) and a focal plane array 122 of light sensitiveelectronic elements. In this embodiment, the focal plane array 122 oflight sensitive electronic elements comprises an array of charge coupleddevices (CCD). The focal plane array may be made of silicon and may becooled. Cooling improves the signal-to-noise ratio of such a focal planearray. For example, the image capture device 130 may be a digital videocamera having a silicon CCD array and be provided with a digitalinterface (e.g., USB or Firewire) or storage media (e.g., a DV tape ormemory stick) for communication of recorded images. Alternatively, thefocal plane array 122 of light sensitive electronic elements may be madefrom InGaAs. As described hereinafter with reference to otherembodiments of the invention, the image capture device 130 may comprisea pixel detector. The pixel detector may be a contact pixel detectorcoupled to the opposite surface of the silicon sample. Alternatively,the image capture device 130 may comprise a pixel detector or an arrayof charge coupled devices (CCD) and a tapered fiber bundle that iscoupled between the opposite surface of the silicon sample 140 and thepixel detector or CCD array 140 or a CCD in contact mode. Other imagecapture devices may be practiced provided the devices are capable ofcapturing simultaneously the induced photoluminescence across a largearea of the semiconductor sample.

Image processing techniques may be applied to the PL images to quantifyspecified electronic properties of the silicon sample 140. Spatialvariations of the PL intensity are checked for. As shown in FIG. 1, ageneral-purpose computer 150 can acquire and analyze PL images recordedby the image capture device 130 via a communications channel 152, whichmay be a suitable communications interface or storage device. The imageprocessing techniques may be implemented in software, hardware, or acombination of the two. The specified electronic properties may compriseone or more of local defect rich areas, local shunts, localcurrent-voltage characteristics, local diffusion length and localminority carrier lifetime. The embodiments of the invention are able todetermine such properties contactlessly. Imaging is distinct fromphotoluminescence mapping, which is slow and therefore not suitable forindustrial application as an inline production tool, and spectroscopictesting of PL, which typically involves testing a small area of asemiconductor. The system in accordance with this embodiment of theinvention can be used to identify defective areas of the wafer 140. Theembodiments of the invention can be used to contactlessly test usingphotoluminescence the silicon structure after each step of processing ofa photovoltaic device. An influence of individual processing steps onthe spatial material quality can thereby be monitored.

FIG. 4 illustrates a system 400 for inspecting a silicon structure 440in accordance with a further embodiment of the invention. In thedrawing, features of FIG. 4 that are like those of FIG. 1 are given alike reference numeral (e.g. the light source 110 of FIG. 1 and thelight source 410 of FIG. 4 have such like reference numerals). Thestructure 440 is again preferably a silicon wafer. To simplify thedrawing, a general-purpose computer is not shown. The system 400comprises a light source 410, a short-pass filter unit 414, and an imagecapture device 422. The system also comprises a collimator 412 and maycomprise a homogenizer 416. A field lens may also be employed (notshown).

Again, the light source 410 generates light suitable for inducingphotoluminescence simultaneously across a large area of the siliconsample 440. The power of the generated light exceeds 1.0 Watt. Lightsources 410 that can be practiced comprise one or more lasers, a broadspectrum light source combined with suitable filtering to provide partlyfiltered light, and an array of light emitting diodes (LED). Other highpowered light sources may be practiced without departing from the scopeand spirit of the invention.

In this embodiment, the image capture device comprises a pixel detector422 and in particular a contact pixel detector 422 coupled to thesurface of the silicon sample 440 that is opposite the illuminatedsurface. The contact pixel detector 422 detects photoluminescenceinduced simultaneously across a large area of the silicon sample 440.The contact pixel detector 422 may have a higher efficiency ofcollecting photoluminescence than the image capture device of FIG. 1.Further the contact pixel detector 422 may have a lower resolution thanthe CCD array of FIG. 1. Also, a long-pass filter may not be requiredbetween the sample 440 and the contact pixel detector 422. The siliconsample 440 may perform this function.

FIG. 5 illustrates another system 500 for inspecting a silicon structure540 in accordance with another embodiment of the invention. Again,features of FIG. 5 that are like those of FIG. 1 are given a likereference numeral. The structure 540 comprises preferably a siliconwafer. To simplify the drawing, a general-purpose computer is again notshown. The system 500 comprises a light source 510, a short-pass filterunit 514, and an image capture device 522. The system also comprises acollimator 512 and may comprise a homogenizer 516.

In this embodiment, the image capture device comprises a pixel detectoror an array of charge coupled devices (CCD) 522, which is coupled by atapered fiber bundle 560 to the surface of the silicon sample 540 thatis opposite the illuminated surface. The tapered fiber bundle 560 mayreduce the area of the CCD array relative to the sample size by a factorof 2 to 3, up to about 10. For example, the CCD array or pixel detectormay have a size of 60 mm×60 mm.

4. Illumination and Imaging on Same Side

FIG. 2 illustrates a system 200 for inspecting a silicon structure 240in accordance with still another embodiment of the invention. In thedrawing, features of FIG. 2 that are like those of FIG. 1 are given alike reference numeral. The structure 240 is again preferably a siliconwafer. To simplify the drawing, a general-purpose computer is not shown.The system 200 comprises a light source 210, a short-pass filter unit214, and an image capture device 230. The system 200 also comprises acollimator 212 and may comprise a homogenizer 216. A field lens (notshown) may also be employed.

Again, the light source 210 generates light suitable for inducingphotoluminescence homogeneously across a large area of the siliconsample 240. The total optical power of the generated light exceeds 1.0Watt. Any of a number of light sources may be employed as the lightsource 210. Details of such light sources are set forth hereinbeforewith reference to FIG. 1.

In the embodiment of FIG. 2, the elements of the system 200 are arrangedas follows: a light source 210 facing the silicon sample 240, thecollimator 212, the short-pass filter unit 214, and the homogenizer 216optically aligned in that sequence. However, other orderings of some orall of these elements may be practiced without departing from the scopeand spirit of the invention. This combination of lighting elements isoff-axis in that the light source 210 and associated optical elementsare oriented at the surface of the sample 240 at an angle of less than90 degrees. The elements are together spaced apart from the siliconsample 240 so that the large area of the sample 240 can be illuminated.The image capture device 230 (and a long-pass filter unit 218) isperpendicularly oriented relative to the surface of the silicon sample240. The long-pass filter unit 218 is needed to remove incident lightfrom the light source 210. Thus, the image capture device 230 capturesphotoluminescence from the same side as that illuminated by incidentlight from the light source 210 to induce the photoluminescence (againindicated by rays or arrows emanating from the surface of the siliconsample 240).

The light source 210 generates light suitable for inducingphotoluminescence in the silicon sample. The total optical power of thegenerated light exceeds 1.0 Watt.

The image capture device 130 in this embodiment comprises a focusingelement 220 (e.g. a lens) and a focal plane array 222 of light sensitiveelectronic elements. In this embodiment, the focal plane array 222 oflight sensitive electronic elements comprises an array of charge coupleddevices (CCD). Preferably, the focal plane array may be made fromsilicon and may be cooled. For example, the image capture device 130 maybe a digital video camera having a silicon CCD array and be providedwith a digital interface (e.g., USB or Firewire) or storage media (e.g.,a DV tape or memory stick) for communication of recorded images.Alternatively, the focal plane array 222 of light sensitive electronicelements may be made from InGaAs. As described hereinafter withreference to other embodiments of the invention, the image capturedevice 230 may comprise a pixel detector.

Image processing techniques may be applied to the PL images to quantifyspecified electronic properties of the silicon sample 240 using thespatial variation of the photoluminescence induced in the large area.The specified electronic properties may comprise one or more of localdefect rich areas, local shunts, local current-voltage characteristics,and local minority carrier lifetime.

FIG. 3 illustrates a system 300 for inspecting a silicon structure 340in accordance with yet another embodiment of the invention. This system300 also comprises a light source 310, a short-pass filter unit 314, andan image capture device 330. The system 300 also comprises a collimator312 and may comprise a homogenizer 316. The system may also comprise afield lens (not shown). The image capture device 330 may comprise afocusing element 320 (e.g. a lens) and a focal plane array 322 of lightsensitive electronic elements. A long-pass filter unit 318 may also bedisposed between the camera 330 and the surface from which thephotoluminescence emanates. The elements of the system 300 are the sameas those in FIG. 2, except that the light source 310 and associatedoptical elements are perpendicularly oriented to the surface of thesample 340. The image capture device 330 (and the long-pass filter unit318) is off-axis in that the image capture device 330 (and the long-passfilter unit 318) is oriented at the surface of the sample 340 at anangle of less than 90 degrees. The image capture device 330 capturesphotoluminescence from the same side as that illuminated by the lightsource 310 to induce the photoluminescence (again indicated by rays orarrows) emanating from the surface of the silicon sample 340.

FIG. 7 illustrates a system 700 for inspecting a silicon structure 740,like that of FIGS. 2 and 3, except that in this embodiment, the lightsource 710 and associated optics 712, 714, 716 and the image capturesystem 730, 722, 720, 718 are both off-axis (not perpendicular) to thesample 740.

The embodiments of the invention can be used advantageously withindirect bandgap semiconductors, which do not generate photoluminescenceas efficiently as direct bandgap semiconductors like GaAs, AlGaAs andmany III-V semiconductors. Large areas including up to the entire areaof a wafer can be illuminated to induce photoluminescencesimultaneously. Advantageously, the entire wafer is simultaneouslyilluminated, which permits faster and more consistent testing. Forexample, a solar cell normally operates when the entire device isilluminated, not just a part of the solar cell. More quantitativedetails of the cell can be obtained in this fashion. While theembodiments of the invention have been described with reference toinspecting wafers to identify defects in the wafers, the embodiments ofthe invention are not limited to such applications. The embodiments ofthe invention can be used to inspect partially or fully formed devicesto identify defects in the devices. The embodiments of the inventionhave more general application to the microelectronics industry.

The embodiments of the invention where the light source and imagecapture system are on opposite sides or the same side of the indirectbandgap semiconductor structure may be used for identifying possibledefects in bare wafers and partially fabricated semiconductor devices.The same-side light source and image capture system configuration may beused to test fully fabricated semiconductor devices, especially whereone surface of the device is fully metallized.

The foregoing describes only a small number of methods and systems forinspecting indirect bandgap semiconductors in accordance withembodiments of the invention. Modifications and/or substitutions can bemade thereto without departing from the scope and spirit of theinvention. The embodiments are intended to be illustrative and notrestrictive.

1. A method of inspecting an indirect bandgap semiconductor structure,said method comprising the steps of: generating light suitable forinducing photoluminescence in said indirect bandgap semiconductorstructure; short-pass filtering said light to reduce long-wavelengthlight of said generated light above a specified emission peak;collimating said light; substantially uniformly and simultaneouslyilluminating a large area of said indirect bandgap semiconductorstructure with said collimated, short-pass filtered light; capturingimages of photoluminescence simultaneously induced by said substantiallyuniform, simultaneous illumination incident across said large area ofsaid indirect bandgap semiconductor structure using an image capturedevice capable of capturing simultaneously said inducedphotoluminescence; and image processing said photoluminescence images toquantify spatially resolved, specified electronic properties of saidindirect bandgap semiconductor structure using the spatial variation ofsaid photoluminescence induced in said large area.
 2. The methodaccording to claim 1, wherein said indirect bandgap semiconductorcomprises silicon.
 3. The method according to claim 1, wherein saidstructure comprises a bare or partially processed wafer of indirectbandgap semiconductor material.
 4. The method according to claim 1,wherein said structure comprises at least one partially formedelectronic device.
 5. The method according to claim 4, wherein theelectronic device is a photovoltaic device.
 6. The method according toclaim 1, wherein said structure comprises a bare or partially processedsilicon-on-insulator (SOI) structure.
 7. The method according to claim1, wherein said short-pass filtering step is implemented using one ormore short-pass filters.
 8. The method according to claim 1, whereinsaid short-pass filtering step is implemented using one or moredielectric mirrors.
 9. The method according to claim 1, wherein saidshort-pass filtering step is implemented using a combination of one ormore dielectric mirrors and one or more short pass filters.
 10. Themethod according to claim 1, wherein said illuminated area of saidindirect bandgap semiconductor structure is equal to or greater thanabout 1.0 cm.sup.2.
 11. The method according to claim 1, furthercomprising the step of homogenizing said generated light.
 12. The methodaccording to claim 1, wherein said method is performed at roomtemperature.
 13. The method according to claim 1, wherein said generatedlight is monochromatic or substantially monochromatic light.
 14. Themethod according to claim 1, wherein said light is generated by at leastone laser, laser diode, laser diode array, or high-powered lightemitting diode (LED).
 15. The method according to claim 1, wherein saidlight is generated by an array of light emitting diodes (LEDs).
 16. Themethod according to claim 1, wherein said light is generated by a broadspectrum lamp and filtered to limit the spectrum of said light.
 17. Themethod according to any one of claims 13, wherein the total opticalpower of said light exceeds about 1 Watt.
 18. The method according toclaim 1, wherein a source of said generated light is oriented toward thesurface of one side of said structure for illumination of that surfaceand an image capture device is oriented toward the same surface forcapturing said images of photoluminescence from that surface.
 19. Themethod according to claim 1, wherein a source of said generated light isoriented toward the surface of one side of said structure forillumination of that surface and said image capture device is orientedtoward the surface of an opposite side of said structure for capturingsaid images of photoluminescence from the surface of said opposite side.20. The method according to claim 19, wherein said structure acts aslong-pass filter of said incident light used for excitation of saidphotoluminescence.
 21. The method according to claim 18, wherein one ormore long pass filters are used in combination with said image capturedevice.
 22. The method according to claim 18, wherein said image capturedevice comprises a focusing element and a focal plane array of lightsensitive electronic elements.
 23. The method according to claim 22,wherein said focal plane array of light sensitive electronic elementscomprises an array of charge coupled devices (CCDs).
 24. The methodaccording to claim 22, wherein said focal plane array is made fromsilicon.
 25. The method according to claim 22, wherein said focal planearray of light sensitive electronic elements is made from InGaAs. 26.The method according to claim 22, wherein said focal plane array iscooled.
 27. The method according to claim 18, wherein said image capturedevice comprises a pixel detector.
 28. The method according to claim 27,wherein said pixel detector is a contact pixel detector coupled to asurface of said structure.
 29. The method according to claim 18, whereinsaid image capture device is a pixel detector or an array of chargecoupled devices (CCDs), and a tapered fiber bundle is coupled between asurface of said structure and said pixel detector or said CCD array. 30.The method according to claim 1, wherein said specified electronicproperties comprise one or more of local defect densities, local shunts,local current-voltage characteristics, local diffusion length, and localminority carrier lifetime.
 31. A system for inspecting an indirectbandgap semiconductor structure, said system comprising: a light sourcefor generating light suitable for inducing photoluminescence in saidindirect bandgap semiconductor structure; a short-pass filter unitdisposed between said light source and said indirect bandgapsemiconductor structure to reduce long-wavelength light of saidgenerated light above a specified emission peak; a collimator disposedbetween said light source and said indirect bandgap semiconductorstructure, said collimated, short-pass filtered light substantiallyuniformly and simultaneously illuminating a large area of said indirectbandgap semiconductor structure; an image capture device orientedtowards said indirect bandgap semiconductor structure for capturingimages of photoluminescence induced by said substantially uniform,simultaneous illumination incident across said large area of saidindirect bandgap semiconductor structure by incident light.
 32. Thesystem according to claim 31, further comprising an image processor forprocessing said photoluminescence images to quantify spatially resolved,specified electronic properties of said indirect bandgap semiconductorstructure.
 33. The system according to claim 31, wherein said indirectbandgap semiconductor comprises silicon.
 34. The system according toclaim 31, wherein said structure comprises a bare or partially processedwafer of indirect bandgap semiconductor material.
 35. The systemaccording to claim 31, wherein said structure comprises at least onepartially formed electronic device.
 36. The system according to claim35, wherein said electronic device comprises a photovoltaic device. 37.The system according to claim 31, wherein said structure comprises abare or partially processed silicon-on-insulator (SOI) structure. 38.The system according to claim 31, wherein said short-pass filter unitcomprises one or more short-pass filters.
 39. The system according toclaim 31, wherein said short-pass filter unit comprises one or moredielectric mirrors.
 40. The system according to claim 31, wherein saidshort-pass filter unit comprises a combination of one or more dielectricmirrors and one or more short pass filters.
 41. The system according toclaim 31, wherein said illuminated area of said indirect bandgapsemiconductor structure is equal to or greater than about 1.0 cm.sup.2.42. The system according to claim 31, further comprising a homogenizer.43. The system according to claim 31, wherein said system inspects saidindirect bandgap semiconductor sample at room temperature.
 44. Thesystem according to claim 31, wherein said generated light ismonochromatic or substantially monochromatic light.
 45. The systemaccording to claim 31, wherein said light source comprises at least onelaser, laser diode, laser diode array, or high-powered light emittingdiode (LEDs).
 46. The system according to claim 31, wherein said lightsource comprises an array of light emitting diodes (LEDs).
 47. Thesystem according to claim 31, wherein said light source comprises abroad spectrum lamp and a filter to limit the spectrum of said light.48. The system according to claim 44, wherein the total optical power ofsaid light exceeds about 1 Watt.
 49. The system according to claim 31,wherein said light source is oriented toward the surface of one side ofsaid structure for illumination of that surface and said image capturedevice is oriented toward the same surface for capturing said images ofphotoluminescence from that surface.
 50. The system according to claim31, wherein said light source is oriented toward the surface of one sideof said structure for illumination of that surface and said imagecapture device is oriented toward the surface of an opposite side ofsaid structure for capturing said images of photoluminescence from thesurface of said opposite side.
 51. The system according to claim 50,wherein said structure acts as long-pass filter of said incident lightused for excitation of said photoluminescence.
 52. The system accordingto claim 49, further comprising one or more long pass filters for use incombination with said image capture device.
 53. The system according toclaim 49, wherein said image capture device comprises a focusing elementand a focal plane array of light sensitive electronic elements.
 54. Thesystem according to claim 53, wherein said focal plane array of lightsensitive electronic elements comprises an array of charge coupleddevices (CCDs).
 55. The system according to claim 53, wherein said focalplane array is made from silicon.
 56. The system according to claim 53,wherein said focal plane array of light sensitive electronic elements ismade from InGaAs.
 57. The system according to claim 53 wherein saidfocal plane array is cooled.
 58. The system according to claim 49,wherein said image capture device comprises a pixel detector.
 59. Thesystem according to claim 58, wherein said pixel detector is a contactpixel detector coupled to a surface of said structure.
 60. The systemaccording to claim 49, wherein said image capture device is a pixeldetector or an array of charge coupled devices (CCDs), and furthercomprising a tapered fiber bundle coupled between a surface of saidstructure and said pixel detector or said CCD array.
 61. The systemaccording to claim 31, wherein said specified electronic propertiescomprise one or more of local defect densities, local shunts, localcurrent-voltage characteristics, local diffusion length, and localminority carrier lifetime.
 62. The system according to claim 31, furthercomprising means for image processing said photoluminescence images toquantify spatially resolved, specified electronic properties of saidindirect bandgap semiconductor structure using the spatial variation ofsaid photoluminescence induced in said large area.
 63. A method ofinspecting a silicon structure, said method comprising the steps of:generating light suitable for inducing photoluminescence in said siliconstructure; short-pass filtering using one or more short-pass filterssaid light to reduce long-wavelength light of said generated light abovea specified emission peak; collimating said light; substantiallyuniformly and simultaneously illuminating a large area of one side ofsaid silicon structure with said collimated, short-pass filtered light;and capturing images of photoluminescence simultaneously induced by saidsubstantially uniform, simultaneous illumination incident across saidlarge area of said silicon structure using an image capture devicecapable of capturing simultaneously said induced photoluminescence. 64.The method according to claim 63, further comprising the step of imageprocessing said photoluminescence images to quantify spatially resolved,specified electronic properties of said silicon structure.
 65. Themethod according to claim 63, wherein said structure comprises a bare orpartially processed wafer of silicon material, at least partially formedphotovoltaic or other electronic device made of silicon, or a bare orpartially processed silicon-on-insulator (SOI) structure.
 66. The methodaccording to claim 63, wherein said short-pass filtering step isimplemented using one or more short-pass filters.
 67. The methodaccording to claim 63, wherein said short-pass filtering step isimplemented using one or more dielectric mirrors.
 68. The methodaccording to claim 63, wherein said short-pass filtering step isimplemented using a combination of one or more dielectric mirrors andone or more short pass filters.
 69. The method according to claim 63,wherein said illuminated area of said silicon structure is equal to orgreater than about 1.0 cm.sup.2.
 70. The method according to claim 63,further comprising the step of homogenizing said light.
 71. The methodaccording to claim 63, wherein said method is performed at roomtemperature.
 72. The method according to claim 63, wherein saidgenerated light is monochromatic or substantially monochromatic light.73. The method according to claim 64, wherein said light is generated byat least one laser, laser diode, laser diode array, high-powered lightemitting diode (LED), an array of light emitting diodes (LEDs), or abroad spectrum lamp and filtered to limit the spectrum of said light.74. The method according to claim 73, wherein the total optical power ofsaid light exceeds about 1 Watt.
 75. The method according to claim 63,wherein a source of said generated light is oriented toward the surfaceof one side of said structure for illumination of that surface and animage capture device is oriented toward the same surface for capturingsaid images of photoluminescence from that surface.
 76. The methodaccording to claim 63, wherein a source of said generated light isoriented toward the surface of one side of said structure forillumination of that surface and an image capture device is orientedtoward the surface of an opposite side of said structure for capturingsaid images of photoluminescence from the surface of said opposite side.77. The method according to claim 76, wherein said structure acts as along pass filter of said incident light used for excitation of saidphotoluminescence.
 78. The method according to claim 63, furthercomprising the step of long pass filtering said photoluminescenceinduced in said silicon structure.
 79. The method according to claim 63,wherein said image capturing step is implemented using a focusingelement and a focal plane array of light sensitive electronic elements.80. The method according to claim 79, wherein said focal plane array oflight sensitive electronic elements comprises an array of charge coupleddevices (CCDs).
 81. The method according to claim 79, wherein said focalplane array is made from silicon.
 82. The method according to claim 79,wherein said focal plane array of light sensitive electronic elements ismade from InGaAs.
 83. The method according to claim 79 wherein saidfocal plane array is cooled.
 84. The method according to claim 75,wherein said image capture device comprises a pixel detector.
 85. Themethod according to claim 84, wherein said pixel detector is a contactpixel detector coupled to a surface of said structure.
 86. The methodaccording to claim 75, wherein said image capture device is a pixeldetector or an array of charge coupled devices (CCDs), and a taperedfiber bundle is coupled between a surface of said structure and saidpixel detector or said CCD array.
 87. The method according to claim 64,wherein said specified electronic properties comprise one or more oflocal defect densities, local shunts, local current-voltagecharacteristics, local diffusion length, and local minority carrierlifetime.
 88. A system for inspecting a silicon structure, comprising: alight source for generating light suitable for inducingphotoluminescence in said silicon structure; a short-pass filter unitdisposed between said light source and said silicon structure to reducelong-wavelength light of said generated light above a specified emissionpeak; a collimator disposed between said light source and said siliconstructure, said collimated, short-pass filtered light substantiallyuniformly and simultaneously illuminating a large area of said siliconstructure; and an image capture device for capturing images ofphotoluminescence simultaneously induced by said substantially uniform,simultaneous illumination incident across said large area of saidsilicon structure.
 89. The system according to claim 88, furthercomprising an image processor for processing said photoluminescenceimages to quantify spatially resolved, specified electronic propertiesof said silicon structure.
 90. The system according to claim 88, whereinsaid structure comprises a bare or partially processed wafer of siliconmaterial, at least partially formed photovoltaic device made of silicon,or a bare or partially processed silicon-on-insulator (SOI) structure.91. The system according to claim 88, wherein said short-pass filterunit comprises one or more short-pass filters.
 92. The method accordingto claim 88, wherein said short-pass filter unit comprises one or moredielectric mirrors.
 93. The method according to claim 88, wherein saidshort-pass filter unit comprises a combination of one or more dielectricmirrors and one or more short pass filters.
 94. The system according toclaim 88, wherein said illuminated area of said silicon structure isequal to or greater than about 1.0 cm.sup.2.
 95. The system according toclaim 88, further comprising a homogenizer for homogenizing saidgenerated light.
 96. The system according to claim 88, wherein saidsystem inspects said silicon structure at room temperature.
 97. Thesystem according to claim 88, wherein said generated light ismonochromatic or substantially monochromatic light.
 98. The systemaccording to claim 88, wherein said light source comprises at least onelaser, laser diode, laser diode array, high-powered light emitting diode(LED), an array of light emitting diodes (LEDs), or a broad spectrumlamp and filtered to limit the spectrum of said light.
 99. The systemaccording to claim 88, wherein the total optical power of said lightexceeds about 1 Watt.
 100. The system according to claim 88, whereinsaid light source is oriented toward the surface of one side of saidstructure for illumination of that surface and said image capture deviceis oriented toward the same surface for capturing said images ofphotoluminescence from that surface.
 101. The system according to claim88, wherein said light source is oriented toward the surface of one sideof said structure for illumination of that surface and said imagecapture device is oriented toward the surface of an opposite side ofsaid structure for capturing said images of photoluminescence from thesurface of said opposite side.
 102. The system according to claim 101,wherein said structure acts as long-pass filter of said incident lightused for excitation of said photoluminescence.
 103. The system accordingto claim 100, further comprising one or more long pass filters for usein combination with said image capture device.
 104. The system accordingto claim 100, wherein said image capture device comprises a focusingelement and a focal plane array of light sensitive electronic elements.105. The system according to claim 104, wherein said focal plane arrayof light sensitive electronic elements comprises an array of chargecoupled devices (CCDs).
 106. The system according to claim 104, whereinsaid focal plane array is made from silicon.
 107. The system accordingto claim 104, wherein said focal plane array of light sensitiveelectronic elements is made from InGaAs.
 108. The system according toclaim 104 wherein said focal plane array is cooled.
 109. The systemaccording to claim 100, wherein said image capture device comprises apixel detector.
 110. The system according to claim 109, wherein saidpixel detector is a contact pixel detector coupled to a surface of saidstructure.
 111. The system according to claim 100, wherein said imagecapture device is a pixel detector or an array of charge coupled devices(CCDs), and further comprising a tapered fiber bundle coupled between asurface of said structure and said pixel detector or said CCD array.112. The system according to claim 88, wherein said specified electronicproperties comprise one or more of local defect densities, local shunts,local current-voltage characteristics, local diffusion length, and localminority carrier lifetime.